fail, MonadFail, or MonadPlus? (was Re: broken Monad Either instance?)

Tyson Whitehead twhitehead at
Fri Dec 9 16:53:49 CET 2011

On December 8, 2011 20:15:57 Iavor Diatchki wrote:
> this is the way things used to be in Haskell 1.4 (if you are curious
> take a look at page 21 of
>  I am not
> exactly sure why the change with the "fail" method happened but I
> think it had something to do with concerns that depending on the
> pattern your program might get a different constraint (e.g. Monad vs.
> MonadPlus).   To me this seems perfectly reasonable I don't know why
> it was perceived as a problem.

That would seem like reasonable behavior to me as well.

Cheers!  -Tyson

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